Ozone Effects on in vitro Biofilm

Ozone is a very powerful oxidizer that oxidizes any organic matter on its way. This property makes ozone a potent disinfectant that is successfully used in food industry, medicine and water treatment. A recently added application is the use of ozone gas in dentistry for caries treatment (HealOzone, USA). Equipment is already used in dental clinics. There are two hypotheses on how ozone works in caries treatment: 1) ozone kills bacteria (including the cariogenic ones), allowing the establishment of a more healthy microflora at the treated site and 2) it removes organic material from carious lesions and enables calcium and phosphate ions to diffuse through the lesions resulting in remineralization. Our aim was to investigate the kinetics and mechanisms of microbial inactivation by ozone. For this, two in vitro biofilm model systems were used: the constant depth film fermentor (CDFF) with mature dental plaque microcosm biofilm and a microtiter plate model with Streptococcus mutans biofilms grown under specific conditions. Chlorhexidine treatment and water treatment were used as positive and negative controls respectively. Both, chlorhexidine and ozone treatments were more effective in killing bacteria in biofilms covering open, smooth surface as opposed to biofilms grown at a stagnation site. The susceptibility of the bacteria to ozone varied according to biofilm age and thickness, growth conditions (feast vs. famine) and metabolic state of the cells during the treatment. Information on the working mechanisms of ozone will provide the rationale for optimal clinical applications.

This work was supported financially by CurOzone, USA.